text:
Is it true that airlines won't let pilots drink diet soda?
I watched a documentary called Hungry for Change that claimed pilot associations advise avoiding diet soda due to the aspartame sweetener inhibiting motor skills and killing brain cells.
Is this true?

If you don't get a good answer here, you could also ask over on Skeptics StackExchange.

Since this page is, literally, already on the first page of a google search for "FAA pilots and diet soda" (I was hoping to find official commentary), I'm going to guess there is not a lot of information on this.  There does seem to be a fair amount of hearsay though...  For whatever that is worth.

"Both the U.S. Air Force magazine “Flying Safety” and the U.S. Navy magazine, “Navy Physiology” published articles warning about the many dangers of aspartame including the cumulative deleterious effects of methanol and other reactions" (source). No idea if this is based on valid elements. On the other hand: Aspartame controversy

Since tomato juice contains more methanol than diet soda, this is quite silly.

Seems like more pseudoscience crap. There is nothing in aspartame that could cause any such effect, beyond the tiny amount of methanol, that (as @DavidSchwartz points out) many other beverages contain more of.

As I retired in 1999, I can't comment on the current situation. However, I can assure you that based on 30 years of flying prior to retirement, I never at any time heard of such.

For the benefit of those not in the US, exactly what is "diet soda"?

@Simon By "diet soda" they mean flavored carbonated beverages that are sweetened with low-calorie (or no calorie) sweeteners rather than sugar or corn syrup. They're typically sweetened with aspartame and/or sucralose.

Appreciate the responses and information from everyone!

I can't find any explicit FAA banning of Aspartame by the FAA so its most likely hype and pseudo science. The FAA did republish an article in one of their briefs that lists it as a food to eat (but they state its not their full official position). This article also states the FAA has no opinion on the matter.
However, the FAA does hold the position that you as the pilot in command are responsible, to some extent for your own health (your chosen airline may also have policy on this). If you as the PIC know that you respond poorly to aspartame then you are responsible for avoiding it. The FDA seems to have done some research on the adverse effects of it and they are at least existent.

The link is not to research done by the FDA but to nonsense sent to the FDA by kooks. The FDA position on Aspartame is that is generally safe.

I've never gotten anything to this effect from my airline nor pilot union, and they'd better start stocking cans of unsweetened Snapple if they were to push this, because I don't like coffee & I most certainly don't want to be drinking lots of sugary sodas to get my caffeine fix in the morning!

There are many pilots particularly from the 1980s and 1990s that have spoken about their experiences of adverse reactions through ingesting aspartame in diet products.
In those days a warning was put out that consuming these products do, in some people, cause side effects.  The General Aviation News reported "pilot George E. Leighton experienced blurred vision so severe he was unable to read instruments on his panels and narrowly avoided a tragic landing after consuming two cups of NutraSweetened hot chocolate prior to his flight." Other pilots who have lost their medical licence because of seizures, tremours and other debilitating effects, have also given warnings about aspartame ingestion.  Pilots such as Captain Harold Wilson, Pilot Haynes Dunn, Texas pilot Charles King and Captain Jim Sells. More recently, you may remember Captain Clayton Osbon flying JetBlue who had a psychotic episode during a flight in March 2012.  He was ridiculed, vilified and his character destroyed for a mental episode that was completely out of his control.  He was known to consume diet products on a regular basis and in fact actually promoted these products.  He is now suing the airline for not pulling him from the flight after he showed obvious signs of being mentally distressed before he boarded the plane.
Aspartame was passed for human consumption in 1981, under a cloud of fraud and deception with Ronald Rumsfeld at the helm of the company G D Searle who discovered the chemical concoction.  It consists of aspartic acid, phenylanaline (two amino acids) and methanol.  Each of these molecules are toxic in their own right. I would recommend that pilots and crew who ingest diet sodas, chew gum, put equal or other aspartame powders in their drinks or sprinkle aspartame powders on their food, beware. Look out for adverse reactions such as headaches, tremours, anxiety, confusion, vision problems, depression, insomnia, dizziness, memory loss, seizures, palpitations to name a few. There are 92 recorded side effects. If you get any of these effects, try stopping aspartame and see if the effects disappear. I have been researching aspartame for a long time now and apart from the dubious way it was passed for consumption, the chemical makeup of this molecule can cause problems for some people. Unfortunately, the warnings that were once given out to pilots, have now been forgotten but it is obvious that pilots are having problems either through fatigue or fatigue exacerbated by aspartame consumption. I can't believe that all the 'pilot errors' that are reported with accident investigations are because of incompetent pilots.  There's something else going on.  If you're a pilot, perhaps it would be best to err on the side of caution and avoid this sweetener.  By the way, it won't help you get slim either!
From 1994-2014, there have been 344 commercial aircraft incidents (16,490 fatalities).  Out of those, over half have been put down to pilot error and nearly 60 to human error.  If there's just a chance you may be affected by this chemical, wouldn't it be prudent not to consume it?  If just one of those 344 incidents was because of aspartame, it's not worth taking the risk that you may have an adverse reaction whilst in the cockpit. Ches Power

also, please add some references, you make lots of claims that need to be backed up by some sources.


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Is it legal to use handheld radios to listen to aviation frequencies in the USA?
Is it legal to use handheld radios to listen to (general aviation) airport frequencies in the USA? Can I go to an airport with a handheld radio and listen to their frequencies?

Yes.  Just don't transmit.

When I first started flying I would often go to the airport during the morning and afternoon rush to listen to the traffic. That way I could practice figuring out where all the traffic was in relation to the airport and what the common ATC instructions were without also having to fly the plane. I still do it from time to time and I use LiveATC.net to listen to frequencies from all over the world from the comfort of my living home.

even if it were illegal, how would anyone possibly catch you?

@sgroves Some years ago, when police radio communications weren't encoded, it was illegal in some countries to have radio receivers capable of being tuned to police frequencies. I don't know how easy was to enforce that. If listening to aviation frequencies were illegal, listening them near an airport could be risky.

@sgroves - many radio receivers use a technology called  a "superheterodyne receiver" which has an oscillator that runs at a frequency similar to but slightly different from the frequency they're receiving (usually it's 455 kHz higher).  These receivers actually broadcast an identifiable signal at that frequency and can be detected quite easily.

There's nothing illegal about listening to public transmissions.

Your receiver must comply with USC 47 302a, the law that says, "you can't interfere with other equipment".
USC 47 301 in general is all about "transmission of energy", or broadcasting.
And it really is beyond the scope of government to say you can't stick a piece of metal in the air and process the signals it receives, provided you don't cause interference to anyone else.
Assuming your radio is receive-only, you really won't have a problem with that. (short of a total malfunction!).

Well, beyond the scope of US government, but not all governments

The question explicitly says "USA".

I think it's just the wording, "beyond the scope of government." That makes me think of government as a concept rather that a specific government. You could just make it "the government" and it wouldn't sound that way

It's not above the scope of the US government, as 18 U.S. Code § 2511 makes it's a crime for anyone to intercept a radio transmission. It's legal to listen into aviation frequencies in the US because the law specifically excludes "aeronautical communications system". On the other hand sticking a piece of metal in the air and listening to the mobile phone conversations it receives can land in you in jail for up to five years.

This is not true: "beyond the scope of government to say you can't stick a piece of metal in the air and process the signals it receives". For a general discussion. For North America specific

Out of curiosity, how could anyone possibly detect if someone's intercepting a radio transmission? It feels like an unenforceable law, intuitively.

@Jules that law is probably invoked to charge individuals who then act on information. Listening and doing nothing is, as you say, very hard to enforce.

Also: TV license detector vans

@Jules In Germany (where listening to aviation radio is not permitted) sometimes officials sneak around in typical planespotter areas and look out for people wearing headphones. It can be so simple. ;-)

Sure you can.  I have an ICOM AC-24 Aviation VHF Transciever in my flight bag and will use it, often when walking around on the apron of untowered airports to be aware of, and communicate with, other aircraft on the ground and in the pattern using the CTAF.
Just be courteous with it and don't use the device to either interfere with ATC communications or for personal conversations with ATC or aircrews.

That reminds me of an airport in Minnesota that I was visiting. Parking for the flight school was on the other side of a taxiway and we had to use a handheld to call ground for permission to walk across the taxiway to the aircraft.

If you don't have the appropriate license and thus can't legally transmit, disable the transmitter. The easy way to do this is to open the radio and remove the little plastic piece that protrudes through the case on the transmit switch. Yes, you could push the switch with a pencil or other item, but disabling the transmit will show good faith that you are not breaking the law and have no intention of doing so in the future.

This seems, well, ridiculous. Should he also puncture the tires on his car to demonstrate that he doesn't intend to intentionally run over someone?

@MPW Doesn't it sound sensible? If you're not supposed to operate a transmitter without a license, one way to prove you're compliant is to show that your device is not (or cannot be operated as) a transmitter.

@MPW removing the tires is a pretty good way to demonstrate that you don't intend to drive the car (which is what you would need license/tax/insurance for). As a bonus, they'd also be the easiest part for someone to steal.

If they are broadcasting on frequencies that are public, then yes, you can listen in. However, you can't interfere with the conversation (broadcasting from your radio, garbling their signal, etc.), because that's a violation of FCC regulation.

It would be good to explain what you mean by "frequencies that are public", and provide a reference for the regulation.

Ah, I see. Sounds good.

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What features are cursor controlled on the A380 Navigation Display?
I read that on the A380 and A350, certain features on the Navigation Display can be controlled via the Keyboard and Cursor Control Unit (KCCU). However, I did not find a full list of these features. I only found the On-Board Airport Navigation System (OANS) and Brake to Vacate (BTV) as examples.
Does it include, for example, selecting elements (waypoints, navaids) for the flightplan with the cursor?

This is what the KCCU looks like:

Source: A380-800 Flight Deck and Systems Briefing for Pilots
Each KCCU is connected to its FMS:

Source: A380-800 Flight Deck and Systems Briefing for Pilots
From the Airbus booklet cited above:

The flight crew uses the KCCU to:
     • Navigate through the FMS pages on the MFD
     • Enter and modify data on the MFD
     • Perform some flight plan revisions on the lateral ND.

And:

The KCCUs enable the flight crew to directly interact with the onside
  ND, MFD and the mailbox section of the SD.

The KCCU can be used, for instance:

To select an airport
To navigate throughout the Airport Moving Map (drag technique)
To set some marks (flags and crosses) for drawing a path
To activate the correct database.

(source: Getting to grip with surveillance
This figure shows what is reachable with the KCCU:

Source: A380-800 Flight Deck and Systems Briefing for Pilots
As there are two KCCU:

Each KCCU displays a different cursor. If both cursors are displayed
  on the SD, only one can be active.

There is a functional redundancy between the keyboard and the cursor control unit.
The Onboard Airport Navigation System which displays a moving airport navigation map, is also accessible using the KCCU interactively.
You may also have a look at the book Introduction to Avionics Systems:

The Multi-Function Display (MFD) displays textual data; over 50 FMS
  pages provide information on the flight plan, aircraft position and
  flight performance. The MFD is interactive; the flight crew can
  navigate through the pages and can consult, enter or modify the data
  via the Keyboard and Cursor Control Unit (KCCU).
The Keyboard and
  Cursor Control Unit (KCCU) enables the flight crew to navigate through
  the FMS pages on the MFD and enter and modify data on the MFD, as
  mentioned above, and can also perform some flight plan revisions on
  the lateral Navigation Display (ND).

Thanks. You mentioned that the KCCU can be used to "set some marks" , "draw a path" and "perform some flight plan revisions" on the ND. Do you have any more specific information about that, because those are exactly the functins I was looking for.

@Jonas87: For the details, the right document to read would be the FCOM, however some elements are available online, e.g. this document in German, translated using Google. Overall, point and click, as well as drag-move is possible with the trackball and validation pushbutton. It is possible to display contextual menu too.

As far as I know the whole FMC (or as it is called in an airbus: MCDU) is controlled by this cursors. So you don't have the limited options by just using scratchpad and line select keys, but you can graphically interact with the items on the screen by using the cursor.

A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern civilian aircraft no longer carry flight engineers or navigators. A primary function is in-flight management of the flight plan. Using various sensors (such as GPS and INS often backed up by radio navigation) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan. From the cockpit, the FMS is normally controlled through a Control Display Unit (CDU) which incorporates a small screen and keyboard or touchscreen. The FMS sends the flight plan for display to the Electronic Flight Instrument System (EFIS), Navigation Display (ND), or Multifunction Display (MFD).
Wikipedia - Flight Management System

thanks, but I was specifically interested in what features can be controlled on the Navigation Display, not the MFD/MCDU. For example, can the cursor be positioned over a waypoint depicted on the ND and then insert this waypoint into the flightplan? Or can the pilot enter arbitrary positioned waypoints via clicking on any position in the ND?

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What is the axis of rotation in a high alpha roll?
When doing an aileron roll at a high alpha (say 25 degs), which axis will the aircraft rotate about?
Is it the incoming air-stream vector or is it more the body X axis? And does the pitch inertial coupling factor into this or is that an unrelated phenomenon?
I am thinking in terms of high agility aircraft like for example the F-16.

That depends on the control system of the aircraft, in case of fighter jets with fly by wire technology and modern fly by wire airliners the yaw control law usually tries to rotate around the velocity vector, which in calm air is the same as the incoming air-stream vector. (according to my university lectures)
The difference in the target yaw rate (r) is just the body roll rate around the x-axis (p) times the tangent of the angle of attack (with the sign flipped, depending on which coordinate system you use).

The F-16 and other fighter aircraft has automatic roll coordination provided by the ARI (Aileron-Rudder Interconnect), or in F-18 it's called RSRI (Rolling Surface to Rudder Interconnect). This function reduces sideslip due to the effect of kinematic coupling caused by rolling the aircraft w.r.t the body X axis, and adverse yaw caused by the deflection of aileron and diff-stabs. This is why it can roll around the flight path, and is also called stability axis roll control.
Without an ARI, the F-16 is bound to have a reversed roll response at 25 deg AOA, according to the LCDP curve from NASA TP-1538.

The F-35 took a step further, as explained in the following paragraph:

To my understanding if the F16 is at 25 degree's alpha for more  than a second  it is very slow(@ 110_120knots in level flight ) with no G's available (one G only) and rolling (is prohibited anyway - to assault two limiters at once, rolling /pitching, but let's do it anyway )now  it is prone to get you into the inertia coupling, anti-yaw rudder kickin now - no pilot input  with rudder pedals- so before that pro adverse yaw rudder but if inertia coupling begin to get into the play anti yaw - opposite rudder is used by Ailerons Rudder Interconnect system ). But let's see if we can arrange for that.The rate of the rolling movements is half from the maximum amount. So it is a small helix (barrel roll) but is no longer around the lift center but more likely to the CG center (so it is a little behind) due Cg position only to the F16(behind the pressure center). In sim the application will not allow any further action (more coupled roll  if you have central tank you can get the upright spin)

.

 The video show slow speed maneuvering

Conservation of momentum demands that the aileron roll is around the body axis (more precisely: the longitudinal axis of inertia). If only an aileron input is made, the result is a rolling moment (plus a bit of yawing from adverse yaw) but no change in pitch.
Proof: Do an aileron roll once without a bit of pitching up before you start aileron input and then with. In an airplane with a regular cambered wing, you need to increase pitch to compensate for the wing's incidence and zero-lift-angle, or your loss of lift will be substantial when flying inverted.
Of course, in an F-16 all pilot commands are interpreted by a computer and will result in movements of all control surfaces, so a pure aileron roll is probably impossible.

"so a pure aileron roll is probably impossible" at slower speed .But at the maneuver speed @440knits it is not a problem .The F16 CAD will do it very fast (@320degrees per second)The problem with F16 is it will deflect the horizontal tails also to do the rolling. The GA aircraft-designed use only rudder to keep the ball centred and ailerons to do it.

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Is it possible to have an afterburner in a turbofan with bypass ratio greater than 1:1?
Is it possible to have an afterburner in a turbofan with a bypass ratio greater than 1:1? At 1.05:1, say, can it have an afterburner?

Is there a reason that 1:1 would seem to be a limit? Look at the GE F101, it's an afterburning turbofan that powers the B-1. The bypass ratio is around 2:1.

@ymb1 while technically saying "no, here's one with >1:1" is an answer, a better answer would also discuss how bypass ratio affects afterburner. There's a reason the F101 is an outlier. I'm guessing there are both performance and configuration considerations. I think we have users who could provide a good explanation, but I might give it a shot later if they don't show up here.

@ymb1 I consider comments free game, I appreciate citing the comment though :) looks like a good start.

Am I crazy, or is a ramjet like the one used on the SR-71 basically an afterburner with an infinity:1 ratio?

@CortAmmon - the SR-71's J58 was first and foremost a turbojet. It has been alternately called a compressor-aided ramjet. turboramjet, and partial-ramjet. Most of the air passes through the compressor before reaching the afterburner.

Higher the bypass ratio, lower the bypass pressure. Lower the pressure, power the after burner's efficiency. This is really not a hard limit.

Can you add reheat to a high bypass turbofan engine?  Sure.  The real question is what is the purpose for doing so?
The bypass ratio of a turbofan is based largely on its operation regime.  Turbojets or low bypass turbofans are excellent choices for operations above Mach 1 to around Mach 2-3.  Larger bypass ratios are more suitable to high subsonic and transonic operations.  Bypass ratios of 3:1 to 5:1 work quite well for transonic operations, for instance the Rolls Royce BR725 engine with a 4:1 bypass ratio, powering the Bombarider Global Express or Gulfstream G650 at cruise speeds of Mach 0.9.  Bypass ratios around 7:1 to 10:1 are great for high subsonic operations around Mach 0.85, which is why they are commonly selected for commercial or transport aircraft which cruise at those speeds.
Reheat offers a lot of thrust, around a 50% increase over max dry thrust, but uses up a lot of fuel, making it unattractive to commercial operators.  Military aircraft are willing to sacrifice fuel efficiency for superior thrust in energy intensive operations like ACM, or takeoff with large payloads.  As military fighters require supersonic flight for either cruise or dash speeds, a low bypass engine should be utilized for this purpose.  Also low bypass ratio engines usually offer a higher engine thrust to weight ratio, in some cases as high as 10:1 versus around 4:1-6:1 for high bypass turbofans, making them very attractive for military applications.
As a result, while it is technically feasible to build a high bypass turbofan with reheat, there is no practical application for it.

I can come up with one reason. You need more power on takeoff than would have without it, but you don't need supersonic speeds (think large capacity freight aircraft).

In the late 60s/early 70s, P&W proposed an engine (the JTF17) for the projected USA Supersonic Transport (SST) which would have introduced afterburning in the fan-generated section of the airflow: a fan-burner.
This doesn't quite match the sense of the questioner's description but you should always beware of assuming that the most trodden paths are the only ones!

This doesn't appear to answer the question.

@Federico, I don't agree that this is a comment. It does answer the question, however the answer could be improved by quoting from official sources such as this which includes the bypass ratio (~1.3 / 1) and a description of the burner.


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How can I continue my flying career in the USA?
I'd like some guidance for my career. I completed my basic CPL from South Africa in 2009 and got a job in January 2015 flying a C208B in Nepal. Now I'm in the USA for more than a year and I'm thinking about continuing my flying here. I have less than 300 hours.
So what do I do now? What is the process to convert my license to an FAA one? What would be a good flying school to join in New York?

Welcome to aviation.SE! This is a Q&A site, not a forum, so we discourage questions that ask for opinions or don't have a clear answer (you can check the [tour] for more information). We do already have a question about validating a foreign license, although if you plan to stay in the US for some years, I strongly recommend getting a full FAA license because they never expire. But validating your SA license might still be a good short-term thing to do.

There are a few things you will need to do to convert it over. You can find a lot of the information on the FAA's website here. This is pertaining to FAA FAR 61.75

Get your foreign license verified by the FAA. This takes 45-90 days and you cant make any moves until this is complete.
Find a local flight school. Once your license has been verified you can start your US training. Assuming you are not a resident you are going to need to get TSA approval to train.
Once you are TSA approved to train you can start to train here. While your hours will count from your previous experience you will still need to pass the FAA written exams and practical exams. As such you will need to learn a bit about general operations here specifically in the US.
Once you have done your training and are prepared to pass the tests and check rides you can schedule them. Your instructor will help you with this.

You will still need to progress through the US certifications PPL->Instrument Rating->CPL and complete all required flight time and tasks to do so. There is no minimum time between check rides so if you have completed all the exams and tasks you can do them all one after another.

This isn't entirely correct. Once you validate a foreign license, you can start flying immediately with no further training or TSA checks required (see this question). But you can only get an FAA private license that way, so if the OP wants an FAA CPL then indeed he will have to go through the TSA/training process.

I had read the question as wanting to convert the CPL over but you are correct.


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How can I calculate the optimum loiter airspeed for an aircraft?
I am in the conceptual phase of designing a 10 seater amphibian aircraft. I have done the initial sizing using Raymer and Roskam's methods. I have got my design point. To do a constraint analysis as well as to find the fuel fraction for loiter phase I need to calculate the optimum loiter velocity for a loiter time of 60 minutes at 7000ft. Breguet's range equation doesn't help since I don't know the fuel fraction of loiter phase. How can I calculate the loiter airspeed?

The optimum cruise speed is the speed at which fuel consumption is minimized per unit of velocity. So, you need to compute the derivative (C/v)' where C is rate of fuel consumption and v is rate of travel (airspeed). (I assume you want this by "loiter". If you want to minimize fuel consumption, that is called "maximum endurance" and that is explained below on the chart.)
Since fuel consumption is proportional to power, and power divided by velocity is thrust, we can graphically determine this point by the thrust required curve. The diagram below shows the relevant relationships:

So, to compute the optimum cruise speed, first draw the thrust-required curve, as shown in the lower part of the diagram above, then you draw a line from the origin tangential to the thrust required curve. The point of tangency lies above the optimum cruise speed on the x-axis.
Maximum Endurance
If by "loiter" your goal is to minimize the fuel flow while maintaining a particular altitude, then you use the power required chart (the upper chart in the figure above). The fuel flow is proportional to power, so the maximum endurance speed is found by locating the lowest point on the power required curve. In the example above, that point is located at 80 CAS. Mathematically, the maximum endurance is found by solving the equation P'=0, where P is the power required function.

To loiter is to stand or wait around without apparent purpose. The loiter speed or holding speed is the same as the maximum endurance speed. So, why not turn it around and make the main answer about the maximum endurance speed and the "bonus" about maximum range. I'd vote you up for it :-)

Would be great if you add your existing approach. Roskam has already an example towards an amphibious aircraft if I am not mistaken.
If you don't have other concerns and if your design is not already constrained by some other points (take off, max speed, etc) here's the first approach:
Several certification regulations enforce a minimum loiter speed that is 1.3 times the stall speed.
Remember that there's a trade off between max speed and loiter speed.

Thanks for your help but I don't have stall speed for my aircraft. To calculate stall speed I will need Clmax and wing area, which I don't know because I haven't reached the wing design phase. To do wing design I need to do constraint analysis so that I can get W/S and hence S i.e wing area. So I am stuck in a loop. What I want to know is if there is any rule of thumb that can give me loiter airspeed when you know empty weight and max take off weight.


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How could a Focke-Wulf 190 pilot see anything at all from his cockpit?
As one can see from the images below, the seat seems to be placed so low on the cabin, I cannot figure out how the pilot could see anything.
Can anyone explain how a Focke-Wulf 190 pilot would be able to see out of the cockpit?

Source

Source

A lot of planes have issues related to this. I remember a few years ago a WWII warbird basically ran over a small plane while taxing because of visibility issues.

Flight sims, like DCS World,  which has a version of the 190, would give you a good idea of the experience if you're interested.


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Why would an ILS installation need a “reflecting surface” around the glideslope antenna?
According to the NTSB, the installation of a glideslope serving runway 11 at KHTS (Tri-State Airport, Huntington, West Virginia) was delayed for over twelve years by the lack of suitable terrain for the glideslope antenna, and, when the glideslope was finally installed (following a CFIT accident involving an aircraft making a nighttime approach to runway 11), these same terrain considerations forced the use of a nonstandard installation utilising an offset antenna (my emphasis):

An instrument landing system was scheduled for installation and commissioning at the Tri-State Airport in June 1958.  The localizer, middle marker, and outer marker installations were completed at that time, but there was insufficient terrain to provide adequate reflecting surface for the glide-slope antenna, within the existing criteria.  Three applications for runway extension, which would also provide suitable terrain for the glide-slope antenna, were submitted to the FAA in Fiscal Years 1967, 1970 and 1971.  The 1967 and 1970 requests were not approved because the necessary “matching funds” from the sponsoring agency were not available, and consequently the Federal funds were not committed.  The 1971 request was still under consideration at the time of the accident.
Subsequent to the accident, concurrent negotiations involving the FAA, West Virginia State Aeronautics Commission, Wilcox Electric Company, Inc., and the Tri-State Airport Authority, resulted in the installation of a nonstandard glide slope for Runway 11, paid for by Federal funds only.  Prior to installation, the FAA estimated that there was a 50 percent probability of success with the glide slope.  A Wilcox Mark I, Series 8020 transmitter was placed 1,211 feet south of the runway centerline and 960 feet west of the Runway 29 threshold.  The elevation of the site was 805.2 feet m.s.l. and the antenna was rotated 13.5° to align with the middle marker.  This offset was required to place the site on suitable terrain, and resulted in an unuseable signal below 1,075 feet m.s.l.  Consequently, there was no reduction in the minimum altitude authorized for the instrument approach.  However, the signal generating capability of the facility to date has been as reliable as standard systems.  [NTSB AAR72-11, page 12 (numbered as 9); the runway has since been extended, and now measures 7,017 feet (and is now runway 12/30, due to changes in the local magnetic declination over time).]

The requirement for “adequate reflecting surface” is surprising; intuitively, one would expect that UHF-radio-wave-reflecting surfaces near your glideslope antenna would be a bad thing, due to the potential for multipath interference from reflected glideslope signals.  Why is this not so?

You ask good, well written questions!

Yeah, by the third paragraph I knew this was a Sean!

@Harper-ReinstateMonica: The third paragraph is me quoting the NTSB...

You wrote that

intuitively, one would expect that UHF-radio-wave-reflecting surfaces near your glideslope antenna would be a bad thing, due to the potential for multipath interference

However, multipath interference is exacly what we want here. The antenna is mounted a certain height above ground and the aircraft receives both the "line of sight" and "ground bounce" signals. These signals create an interference pattern with maxima and minima at certain elevation angles.
There are two antennas mounted at different heights, so that the interference pattern of one antenna is stronger at 0-3° elevation and the other is stronger at 3-5°. Behavior at higher elevation angles is undefined and there are typically some more maxima and minima with a possibility of "false glideslopes", which is why you always approach the glideslope from below.

Nice answer, but I'd like to add that the false glideslopes are not the only reason to capture it from below. And unfortunately it's not always done, see e.g. the Turkish Airlines flight 1951 crash near Amsterdam.

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text:
Why does the DHC-6 pitch down when the flaps are retracted, rather than up?
Air Moorea Flight 1121 crashed because one of its elevator cables broke immediately after the pilot retracted the flaps, but before he could trim out the resulting pitch-down moment - to quote the English translation of the BEA report,

The operator called for the reduction in engine RPM before retraction in order to mitigate the pitchdown moment caused by the flap retraction and so that the right hand, after having positioned the flap control lever on 0°, could be placed be placed on the elevator trim in order to reduce the effort on the control column. [report page 17/PDF page 19]
...stick free, the flap retraction led to a pitch-down moment varying the aeroplane trim between 20° and 30°, the rate-of-climb indicator going to stop at less than 3,000 ft/min and speed reaching 140 kt in twenty seconds… [page 42/44]
In flight, the loads on the cable are at their greatest when it is necessary to counter the pitch moment induced by the retraction of the flaps. [page 61/63]
The malfunction occurred at the top of the initial climb, passing through 350 feet, when the pilot retracted the flaps then adjusted the engine parameters. While he was adjusting the parameters with his right hand, he was holding the wheel with his left hand while pulling back to counter the pitch-down moment and stabilise the airplane on its flight path. It was only at the end of this process, which lasted nine seconds, that he would adjust the trim.
[...]
The flight tests showed that during flap retraction, when pitch control is free, the airplane dives with a high pitch angle. [page 63/65]

and, finally,

The DHC6 Twin Otter has significant pitch-down moment when the flaps are retracted. [page 67/69]

How can this be?  Flaps extend downwards from the trailing edge of a wing, and, thus, should always produce a pitch-down moment when extended (like applying nose-down elevator, except with a much shorter moment arm), and a pitch-up moment when retracted.  Why is the DHC-6 different in this regard?

The Twin Otter isn't unique.  Flaps have varying effects on different airplanes.  Some pitch up with flaps extended, some pitch down.   The pitching moment from flaps isn't just from the nose down moment from the increase in airfoil camber; it includes effects of increased downwash on the tail, which creates a pitch up moment, and to some degree, changes in the vertical aerodynamic center resulting from adding drag up high or down low (like the mild pitch down moment caused by gear extension).
In the Twin Otter the double-slotted flaps are extremely powerful and create a very strong downwash increase at high angles as opposed to just mostly turbulence you get with simpler flap setups. The result is the net effect of flap extension, with the high wing and the location of the horizontal stabilizer, is pitch up because those forces are stronger than the nose down moment created at the wing itself by the camber change.


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What is the "Dying Whale" sound of F-35C during pattern/terminal area operations?
I live near an airbase that just recently started operating F-35s. The variant is the F-35C Lightning II of the Marine Corps.
During operations near the base there is a distinct sound that - for lack of a better description - sounds like a dying whale. The sound can be heard during a touch and go in this video at 2:52. It lasts for less than a second, is a "droning" sound that goes from a tenor to baritone (... really struggling to describe this...). It seems that it might be limited to the F-35C; I was not able to find any evidence of F-35B or F-35As demonstrating the same sound.
My questions are:

What causes this sound?
Why is it only audible during certain flight phases?
Is it correct that this is limited to the F-35C?

sounds like some kind of brief resonance.  Compare to the sound of blowing air across the lip of a bottle.  Could be something that comes up as the engine revs through a critical RPM.  Just a SWAG though.

I second that. It’s just a resident of fact of air flowing through the inlet ducts at certain speeds.  Many fighter airplanes make similar noises when starting, the F-15, F-16, and F-18 all do it, just to name a few.

Oh, this is very common in my opinion.
I live in the approach path to runway 27 at VABB (Mumbai) airport and the newer Airbus A320NEO planes that fly here make a very similar noise but for much longer durations at a much higher amplitude. The PW1000G engines are known for these noises. It occurs during lower-speed operations and I can only hear it during landing (albeit I can't see or hear takeoffs from my house). The exact cause for the noise is low power transient combustion tone caused by pressure changes against the combustion structure. All engines can do this but the geared turbofan of the A320 and A220 have a propensity for it. I don't think PW manufacturing the F35 engines has anything to do with it. This is only limited to the low-speed parts of flight since it needs the turbines to be at a considerably slower speed to get the right resonance frequencies.
It can happen during startup too
Here's a video of this noise (A220) -

That might be correct. There is also another possibility that this may be intake howl (like on Vulcan), which according to Wikipedia is due to the geometry of the inlet.

@AdityaSharma I think these are related phenomena... not sure though. Intake howl happens at around 90% throttle as written on Wikipedia, the title of this question says it's happening during terminal operations too

That 90% is specifically for the Vulcan; different intakes would certainly have different air flow rates at which they produce a howl

@AdityaSharma, yeah you are right


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What is the typical length of a Transport Category Aircraft Maintenance Manual (# of pages)?
This FAA publication contains the following image:

The numbers it lists translate to some very long manuals:

1998: 43,071,266 pages/2,532 manuals = 17,010 pages/manual
2008: 184,068,439 pages/5,500 manuals = 33,467 pages/manual

This seems like a lot. 33,000 pages printed out is nearly 11ft on a shelf (that's 3+ meters for those of you not using medieval units)!

Well, 30 or so chapters with maybe 200-500 pages per in the AMM,  then Component Maintenance Manuals, Wiring Diagram Manuals, Structural Repair Manuals, MMEL, MMEL Document Deviation Guide, Illustrated Parts Catalogs, and some others I can't think of right now.... ats'a lotta pages!  The manuals set for an airliner model will use up a wall of shelf space in a small storage room.


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Have there ever been any JATO bottles using only kerosene?
I've been reading about the early rocket work during WW2. They tried all sorts of fuels, hydrogen peroxide, hydrazine, red fuming nitric acid...
Just in the scope of JATO/RATO, has there ever been one working just with kerosene? The airplane would accelerate normally to sufficient airspeed such that enough oxygen was flowing, then the JATO would ignite. This would then boost the aircraft very rapidly up to a high altitude.
I think this could be called an afterburner all by itself (without the turbojet lol), or maybe even a ramjet all by itself. Whatever you call it, it has no moving parts other than a fuel pump. So I am wondering if this concept was ever tried during WW2 or shortly thereafter.
(P.S., surprised there is not JATO tag, nor RATO tag. I will create it but also use "takeoff" for visibility purposes.)

For a rather complete overview of early rocket fuel work, see Ignition! by John Clark.

C-130's were all built equipped for JATO, but during the time I flew them (1990's) only the Antarctic birds on skis and the Blue Angels airshow bird actually used them. Part of the reason that nobody else did was that carrying around the solid rockets -- Class B explosives -- would be a pain in the neck for little benefit (if you can get in to the field, you can probably get back out again unaided just fine). Kerosene is abundant on the Herk (fuel tanks), but LOX being piped back to mix with it, on command, would be a MAJOR undertaking, with catastrophic results if things go wrong!

Hm -- speaking of Antarctic C-130s...why are JATO bottles so common on them?

@marius, much of antarctica is at an altitude of ~2000 to 3000 meters and so to furnish adequate takeoff performance, the rocket boost is frequently needed.

A RATO unit's purpose is to give a high impulse very quickly, it does this by combining a fuel with an oxidizer causing rapid combustion in a chamber, and forward thrust from the equal and opposite reaction. Kerosene is a fuel, but without an oxidizer you don't have a rocket, you have some lamp oil burning. If you wait until the airplane is moving then it's lamp oil burning in a wind, giving you no benefit.

-1, "lamp oil burning in wind" is a poor description of an afterburner or ramjet. Those too use kerosene "without an oxidizer", yet provide enormous thrust. Indeed, the ramjet can be started at takeoff speeds, and the ram effect will tend to increase both speed and thrust even beyond Mach 1. Also note that afterburners are effectively used like JATO/RATO, just not discardable. They turn on afterburner at launch on a carrier. So "lamp oil burning in a wind, giving you no benefit", is clearly false.

@DrZ214 An afterburner relies on hot, high-pressure oxygen compressed by the jet engine. It does not have "no moving parts", but rather relies on the largest and most complex moving part on the whole aircraft. It would not work if the engine was shut down, when that happens we call it a tailpipe fire.

@user71659 Okay fair enough. I still maintain that a properly designed ramjet can be ignited at takeoff speeds and provide more and more thrust even beyond Mach 1.

@DrZ214, ramjets compress air using forward motion, you need considerable speed to start one. Are you thinking a pulse jet maybe? Those work without forward motion but have low impulse, you don't get much that much thrust.


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Why do air forces still use bombers?
Something I have wondered about recently, since the advent of ICBMs what is the point of long range bombers like the B-2? I understand they have longer range and can carry more payload but wouldn't they be easy prey for fighter jets or SAMs? Surely missiles are a much more attractive option. I don't get why effort and expense goes into bombers.

Given the low radar signature, they would be "easy prey" for fighter jets that will do a quickstart after the bombs dropped, and you would need many of them even for a single bomber, because you have to find him first. Plus, the bombers are not alone, There are always coalition fighters around that bomb enemy airbases and landing strips to prevent enemy fighters from starting at all.

The key requirement for the B-2 was to penetrate hostile, well-protected air space and take out mobile rocket launchers and their garrisons. The B-2 is insanely stealthy for a variety of passive and active reasons.

There's a middle ground: use air-launched missiles from a much simpler bomber (e.g. B-52). On a 10.000 km strike mission, there's 9000 km which needs neither the speed of an ICBM nor the stealth of a B-2.

@MSalters yes, and those missiles (ALCM and SRAM 2) have since been retired... The USAF is back to dropping gravity bombs only.

@jwenting Um, no...  JASSM is still in production, and I think the JSOW is too.

The Maveric Missile (of Desert Storm fame) is also still in production:  http://www.defenseindustrydaily.com/raytheon-restarts-production-of-laser-maverick-missiles-05397/

@DanNeely Maverick isn't compatible with the B-52...

@user19555 talking about the nuclear mission mostly, as the question was about ICBMs.

@jwenting I am not sure you are right about that.  The USAF is back to dropping gravity bombs only  Granted, PBM's provide a lot of capability, but IIRC there are still some long range cruise missiles in the inventory.  (It's been a few years, I'll do some digging around).

And what the future holds ... low observable

@jwenting - (ALCM and SRAM 2) have since been retired... The USAF is back to dropping gravity bombs only Half-right. SRAM 1 is indeed gone (SRAM 2 never entered service), but ALCM (AGM-86B) is still in service (500+ in inventory) and likely won't retire till ~2030 when it'll be replaced by the LRSO. You might have been thinking of the ACM (AGM-129), which was retired just a few years ago. So USAF has and will have nuclear cruise missiles for the foreseeable future.

Once you launch an ICBM, you're pretty much committed.  Even if there is a self-destruct on the missile (I don't know, nor am I making that claim.  Additionally, I think debris from such an act would be a big concern.).  A bomber also allows you to send something part of the way, and rattle your sabers in the face of the other party without again having committed to the act of the warhead being launched.  You can always recall a bomber without having to worry about a debris field or other unintended consequences.
As to the claim that bombers are particularly vulnerable, there are numerous ways they get around this.  For instance the B-2 employs stealth to get around this.  The B-52 can use standoff weapons to reach out to a target (such as cruise missiles or JASM).  Also, the B-52 can use low altitude routes to avoid radar and detection (if you’ve never seen a B-52 do a low level, I recommend you find a route and observe, it’s something else).  And on top of all that, the aircraft have defensive systems to help them on their missions (chaff, flares, RW gear, etc.).
Also, with a bomber, you can employ different types of weapons that give you a broader range of response options.  You can use bombs of anywhere from a 250lb laser/GPS guided bomb to something much larger.  These delivery mechanisms are generally much more accurate than a TBM (Theatre Ballistic Missile) or even an ICBM (InterContinental Ballistic Missile).  Those systems are generally inertially guided (some have GPS capability), which can lead to a larger CEP (circular error of probability), meaning that it may not hit exactly where you aim.  Those systems rely on a much larger warhead to get the job done than bombs from a bomber.  You don't use a Nuke to swat a mosquito, as a bit of military wisdom goes.  And, even ballistic missiles can be intercepted by systems such as the Patriot, so they are not a panacea against being stopped.

I'm not sure if any of them still use it or not, but some ICBMs used star charts for in-flight guidance in addition to their INSs. This allowed them to continually correct for the errors that built up in the inertial navigation systems over the course of the flight. The advantage of this over GPS is that it doesn't stop working if the GPS system gets shut down or destroyed in a global nuclear war (which is the designed use case for pretty much all ICBMs.) I think this method actually predates GPS, though.

@reirab you are correct.  The celestial navigation updates are good up to a point.  However, it is still not as precise as a 1.064 laser designation on the shorter range weapons. Once the ICBM or TBM warhead goes into terminal phase, the chance and ability for a course correction is reduced.

Yeah, obviously using star charts doesn't work for shorter-range weapons, unless you only plan to operate them on clear nights. :) They work for ICBMs because they spend a good deal of their time above the atmosphere. You're definitely right that it's not nearly as accurate as laser designation (or even GPS when it's working,) though.

@reirab - You actually can use star charts during the day. For instance, the SR-71 had a day/night star tracker that referenced some ~60 stars. Obviously, the SR-71 predates GPS, as do most long-range systems: bombers, ships, subs, cruise missiles, etc.

It's about cost, precision, load, time to target, and risk of nuclear war:

Cost: ICBMs are very expensive, even compared to a B2 bomber as a B2 can be reused over and over
Precision: 100 meters or so may not make much difference with a 500 kiloton nuke, but with a 500 pound bomb it's the difference between a hit and a miss
Load: an ICBM doesn't have that much lifting capacity, they are designed to carry nuclear weapons which aren't particularly heavy. A B2 can carry up to about 40,000lbs of payload and a variety of conventional bombs at the same time, that's much more than the heftiest ICBM
Time to target: an ICBM's suborbital path takes at least 15 minutes from launch to target, and that's once you get authorization and build a targeting package for it, which all takes time. A great deal can happen on the battlefield in just 15 minutes, so conventional ICBMs only make sense against strategic targets which won't move, and where time is not a factor. A bomber can loiter on site for hours waiting for targets of opportunity to present themselves, or provide air support for troops on the ground. Long-range missiles are no good for that
Risk of nuclear war: ICBMs were designed for one purpose - nuclear exchange. Several nations have entire defense establishments for the purpose of tracking ICBM launches and responding to them. These nations would need to be notified of a conventional ICBM launch so that they don't react by launching their own nukes. Plus, what if their notification system doesn't work and not everyone gets the message? You'd need an extremely good reason why you would want to risk that!

That doesn't mean that conventional ICBMs don't exist, they may have been developed by now in the Prompt Global Strike program in the US. This uses existing launchers but replaces their nuclear payloads, which is relatively low-cost as the launchers have been developed and tested. It may be a useful capability but it would be unlikely to be ever used due to the risks involved.

would be +1 but is -1 but for the claim that there are conventional tipped ICBMs. There's no point in such, the damage done is not worth the cost of the missile, nor are they accurate enough to have any chance of hitting a target small enough that a conventional warhead would have a chance of destroying it at intercontinental ranges.

@jwenting, the US has an active program in place to build these, whether or not they have been completed or not is open to debate as it is classified. I said they probably exist, not that they do for sure.

no, there were some studies to retask some Minuteman missiles and redevelop the Midgetman but those were dropped as unfeasible and too expensive (plus it'd be impossible for verification purposes for SALT and START). The Chinese have some IRBMs tasked in an anti-carrier role that may or may not be conventional tipped (the consensus seems to be they're probably nuclear) but not ICBMs.

Even so, if you launch a "conventionally tipped" ICBM at someone they are going to assume a nuke, and launch back before you destroy their launch ability.

Oh yes, I can't see a conventional ICBM being launched at a country with nuclear weapons. It would be risky launching one in the general direction of a country with nuclear weapons!

Short Answer: Because not every war or military mission needs an ICBM
On the practical level, some air forces still use bombers because large payloads of standoff weapons like air launched cruise missiles are a desirable military option.
Longer Answer
Your question assumes a single form of military action: a nuclear attack delivered by either an ICBM or a bomber.  It's not an Either / Or proposition.
There is a whole lot more to the use of military force, and the threat of using military force, than that simple binary condition.  To ask that question is to fundamentally misunderstand the purpose behind both a bomber and an ICBM.  The ICBM and the bomber fulfill two distinct military requirements.  Military options are exercised by national political leaders, and national leaders always want options.  An ICBM option menu is "nuclear war or not."  Bombers provide a lot more options.
All an ICBM can to is make a nuclear attack.  That's it.   (Its deterrent role is a different matter, but any competent military force provides a form of deterrence ...)
Bombers are multi-purpose war planes.  They can carry bombs for a nuclear strike, but they can also carry bombs (or other payloads) for a host of other missions.

The classic example is the B-52.  A squadron of B-52's could be on alert during the Cold War, armed with nukes that could be used (but thankfully never were).  At the same time, B-52's form other squadrons were in Viet Nam dropping conventional bombs in a war that was not nuclear.
The B-2 likewise has already been deployed to make conventional
attacks, but it could (if need be) make a nuclear attack.  In that
case, however, ICBM's are either already in play or are likely to
come into play once the nuclear weapons are used.  It's a huge
risk and I hope it never comes to that.
A third example are the Russian Bear (TU-95) and Badger(Tu-16) bombers that were deployed a lot by the USSR during the Cold War.   They were generally equipped to launch cruise missiles, not bombs, and could carry quite a few of those missiles.  That weapons load takes the problem of fighter screen penetration and SAMs out of the picture and makes forces the opposing forces deal with a saturation raid of air -to-surface missiles.  (That particular problem is why the USN developed the AEGIS radar/weapons system).  The USAF also developed a family of long range cruise missiles that do something similar, and which are deployed on bombers.

Bombers are one of the cornerstones of the Nuclear Triad.  Along with Intercontinental Ballistic Missiles and Sumarine launched nuclear weapons, nuclear bombers provide the Nuclear Triad with three levels of redundancy, preventing a total disablement of our nuclear strike capability and ensuring a nuclear retaliatory capability for mutual assured destruction in the event of an nuclear attack on the United States.

Bombers are used much less then they used to be in the piston era. But ICBMs are not the replacement except in nuclear deterrent role. ICBMs are for nuclear attacks only (as already explained in the other answers). In most other roles bombers are replaced by:

Fighters/attack aircraft. A flight of smaller aircraft can do same or more damage than a large one and they have more options evading or even defending against various threats.
Cruise missiles. They are not any faster than fighter, but flying 100 ft above ground level they are extremely difficult to detect and intercept.
UAVs. While they are no match for a fighter and don't have as large payload, they can also fly very low to avoid detection, some are additionally stealth and it's less of a problem if one is lost.

Where bombers are still useful and will likely remain is surprise long-range missions. Bombers can strike almost anywhere in the world from their home base with some aerial refueling. That can be prepared quickly and without having to move many units to forward bases which could warn the enemy. While fighters are also capable of in-flight refueling, they would need to refuel more often and they have no provision for crew rest. B-2 missions often take 30-40 hours.

Lots of other good answers here, but in the interest of getting a bit more global:
Let's say you're Angola and you're trying to set up your own air force after gaining independence from Portugal in 1975.
Is anyone going to sell you some ICBMs?  Yeah, someone might, I guess.  But you should probably keep shopping around.
Eventually you get the Soviets to sell you some fighter/bomber Fitters in 1982. Later on you buy more from Belarus and then Slovakia.
You use them in a couple of civil wars, which is the sort of role that ICBMs are not really well-suited to.

Aside from the cost, there is no way to tell if an ICBM is carrying a nuclear warhead or a conventional warhead. It would be very easy to spook a major power into misinterpreting intentions if a nation goes firing off a bunch of ICBM's.
We call China up and say that all those ICBM's we just shot off aren't carrying nukes, and are aimed at N Korea and not you... I don't think they'd take that explanation at face value. I wouldn't.
Really, not a smart thing to do. The consequences of misunderstandings could be severe.
Cruise missiles, such as the Tomahawk, have been used in very high risk situations where a downed aircraft and a captured pilot would be politically costly. However, cruise missiles can't deal very well with changing situations.
A cruise missile can't tell if civilians have drifted into the target area, and abort the mission or choose another target. A pilot in an aircraft with eyes on target can.
It appears likely that larger remotely controlled drones may take the place of some cruise missiles, as they do put eyes on target prior to attack... until an adversary learns how to jam the drone's data link.

Where the B-2 is concerned, one must first look at the original contract, calling for 132 aircraft.
Relevant as, not unlike our current Ohio and Virginia Class submarine force -  the B-2 proposal approved and signed by Jimmy Carter outlined - among other things at any given time fifteen B-2 would be airborne. This deployment - in and of itself the proverbial "Game Changer" - was to be in place seven days per week, 365 days per year, 24 hours a day. As for the other bombers mentioned in this thread, understand that the B-52 cannot - and never has been able to - launch with a full payload of ordinance AND a full complement of fuel - Its one or the other, the political fact that taxpayer funds have been wasted on upgrades for this old dog for decades notwithstanding. Further, understand that after receiving his B-2 briefing and consulting with Joint Chiefs, Mr. Carter cancelled the dog known as the B-1 Lancer in order to go forward with full program development and production of the B-2. Like the B-52, the Lancer is incapable of launch with a full ordinance payload coupled with a full load of fuel; both need refueling not long after takeoff should the sortie require it.
With the incomparable range of the B-2 lifting body design - it can circumnavigate the planet with but two refueling's - its incredible air-frame strength, making it our only bomber capable of takeoff with both a belly full ordinance and a full load of fuel, and the current lethality of 21st century JDAMs coupled with the new GBU-39 - of which the B-2 can carry 88 - the other aircraft in the U.S. inventory aren't in the same ballpark. Heck, it isn't even the same sport!

golf clap even though I spent some time in the real deal working with Bones who did a great job for us.

It matters little if a buff or a bone launch with a full fuel load or refuel after takeoff. Both bombers operate out of bases that also have aerial tankers. While it is an antique, the buff is also a very cost effective way to get a whole lot of ordnance on target. They're paid for, and their maintenance procedures were worked out decades ago. Unless one is penetrating airspace that is defended with the latest AA systems and those systems haven't been suppressed by prior attack, it doesn't make much sense to send one of our few B2's and risk an operational loss, when a buff can do the job.

Yeah, it does matter....A Spirit goes full stealth in the barn on Guam, our own people - or NATO for that matter - don't know where it is. Subsequently, there are no KC's with which to link it. Remember the Chinese embassy during the Balkans campaign?....The money spent on those old war dogs should have gone to B-2, anybody who worked in the industry - not enlisted or any other AF personnel - know the real deal. Like the Tigershark burying the F16 and the YF23 burying the 22, its politics babe....Go out to AF Plant 42 and watch some truth....


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How much performance penalty is incurred from a WW2-era folding wing mechanism?
I'm interested in WW2-era single-engine piston-prop monoplanes. I'm interested in the folding wing mechanisms from the perspective of performance, chiefly two things:
How much extra weight does it add?
How much extra drag does it add?
I did see this pdf about the sto-wing, but the only thing about weight is

The initial STO-Wing design was operated with hydraulic cylinders, but the added weight of the system reduced performance, so a lighter manual system fitted with safety locks was selected for production.

Wikipedia's folding wing article is pretty short, both in words and in data. It did lead to 2 external links.
This article has no numerical data on the sto-wing, but does cite some book: Richard Thruelsen. The Grumman Story. New York: Praeger Publishers Inc., 1976. 125. I was able to find it on Google Books but it looks like you can't search things there like you used to. "Folding Wing" and "Sto-wing" returned very limited results.
The other link is a dead link.
I really hope someone knows where to find these numbers. It would be really nice to see just how much weight goes into this mechanism. To me it seems pretty significant if you're gonna have a strong pin to make sure the wing won't snap-fold in flight, almost like you need another main wing spar in the joint.

Related


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How does Kalman filtering work in inertial navigation systems?
As far as I understood it correctly most INS-systems use a Kalman filter to compensate measurement errors.
I would like to know:

Does the Kalman filter compensate the errors from all the onboard sensors?
IIRC the Kalman filter is a tracker, that predicts future computation values. How is this useful here?
Is this used on IRS as well? Or only on older INS?

Thank you

See page 27 of Introduction to Inertial Navigation and Kalman Filtering

First you need to understand that observations, or measurements has noises, or errors. Prediction is useful because it gives a reasonable estimate of the present state based on previous data. Say your measurement gives you a very big value but the kalman filter tells the state can not change that fast based on it's knowledge of the system's model, then it will reject reading and bias towards the estimate. Kalman filer receives a vector of inputs of different orders, combing locations, speed, acceleration readings will improve the estimate.

First of all you should  know that a Kalman filter is a state estimation technique. More than a filter, it is an estimator. Whilst it does filter sensor noise in the process, the most important use is to estimate the state of a system.
The KF uses a mathematical model of a system (e.g. an aircraft moving over the earth) to estimate the state of the system (e.g. position, attitude, velocity) by comparing successive measurements to the values that were expected based of previous estimates of the state.

Does the Kalman filter compensate the errors from all the onboard sensors?

No. Firstly, there are many sensors on board, not all are used in Kalman filters. Secondly, you can't fully compensate for all errors, there will always be residual errors in the output.

IIRC the Kalman filter is a tracker, that predicts future computation values. How is this useful here?

It can be used as a tracker indeed. The KF uses its current estimation of the state of the system to predict the state at the time of the next measurement. The differences between the predicted measurement and the actual measurements are then used correct the estimation of the state and update the state uncertainty model.

Is this used on IRS as well? Or only on older INS?

Yes, the KF (usually a more advanced form such as EKF or AKF) is used to fuse data from the multiple sensors is the IRS. In an ADIRU, not only measurements from accelerometers and gyroscopes are used, but also pitot tube and static port measurements are fused in.

I have read somewhere that a Kalman filter is also used for the GPS on aircraft. Is that correct? I would have expected that GPS nowadays work very well and don't have that much errors...

How do you think that GPS receivers comes up with these accurate position estimates? Exactly, Kalman filtering :-)

Can the downvoter please explain their reasons for the -1? I'd be happy to learn what I can improve.  Thank you.

A Kalman filter is used on all kinds of IRU's and INS's, even with airspeed information as in an ADIRU.  A Kalman filter is just a general method (and a very useful one) for state estimation and sensor fusion, which is exactly what's going on in an INS system.  I wouldn't call this "compensation". Inertial naviagation requires us to read in sensor values like angular acceleration, direction of magnetic north, longitudinal acceleration, and even airspeed, then convert those into more meaningful values like ground speed.  If done correctly, these processes (called sensor fusion and state estimation) will minimize errors on all the sensors you feed into it.   That's the quick version.  For a longer explanation of how it works, read on.
Kalman filters are used for sensor fusion and/or state estimation.  State estimation is when the basic physics parameters we want to know like speed and position (called the state of the system), are different from the sensor values we're getting, like magnetic compass readings and gyroscope values.  State estimation problems attempt to estimate these values like speed even in tricky situations like when errors are present or when the state can't be directly computed from the sensor values.  State estimation in Kalman filters can also take into account inputs to the dynamical system like airplane thrust and aileron position to try to improve the accuracy of the model, but this is not necessary and I'm skeptical about how often this is used based on my experience.
Sensor fusion, on the other hand, is when we want to combine several sensors to try and get a sensor that has the best of both worlds.  Sensor fusion and state estimation can overlap. A classic example is GPS and accelerometer sensor fusion.  GPS gives accurate position, but only down to a few meters and may not update at the rate desired. Accelerometers give accurate accelaration values even at small scales, but their position estimate tends to drift over longer periods of time.  By combining the two we can get the precision of INS but with no drift. One advantage of a Kalman filter is that the different sensors being combined don't need to be measuring the same values as long as we have equations for how the sensor values and the internal state are related.  For example, we can combine magnetic compass and gyroscope values even though the two aren't directly analogous. Sensor fusion can also be done with other methods like a complementary filter or Bayesian/Markov methods.
How does a Kalman filter work?  First a Kalman filter estimates the state (say, position and speed) using a system model to predict what the new position should be based on previous values.  This is the new predicted state.  The filter then looks at the sensor values to see what the new position should be based on those measurements.  It then reconciles the predicted and measured position to get a new position estimate based on the fact that both of those values may be inaccurate. The filter does this all including weights based on which errors in measurement and estimation are largest and which errors tend to be correlated with each other.  Note that this includes errors in both estimation and measurement: outside forces and inaccuracies in our model can throw off our prediction step just like bad sensors can affect our measurement step.
Technically the six degree-of-freedom equations often used for inertial navigation are non-linear (which is kind of like saying we can't scale, add, and reorder these transformations and rotations).   A regular Kalman filter will not work in this scenario and the Kalman filter must be a non-linear filter like an extended or unscented Kalman filter.
Kalman filters have several advantages over other filters like a complementary filter.  In elementary situations they can arrive at an identical solution to a similar complementary filter or averaging filter.  You mention tracking while predicting future values, and I'll explain why a Kalman filter helps.  If our last three positions were 1.0, 1.5, 1.7, and 1.8, a simple filter might average 1.7 and 1.8 or similarly try combine past and current values.  This would produce a lag behind the current value.  Kalman filters (and some simple filters) extrapolate previous values to predict the current value more accurately.  Kalman filters really begin to shine as the system we're trying to track changes in complex but predictable ways.
Simple filters like complementary filters struggle more than Kalman filters when errors are correlated or have different weights.  Kalman filters use weighting in their estimate to compensate for correlation in errors and also to give the most bias to the best sensor values.  For example, if angle of attack and airspeed tend to have the same inaccuracies at the same time, or if the gyroscope is much more accurate than the magnetic compass, the Kalman filter will give the sensors weights to compensate for that. If you're in a situation where you can model the equations of motion, or if you know something about the different types of noise in your system, the Kalman filter is probably more accurate than simpler alternatives.
Despite the accuracy of Kalman filters, I've seen a few places where simpler devices like complementary filters were used instead of Kalman filters.  Why?  The main reason is complexity, which I won't elaborate on too much at this point.

A Kalman filter reduces noise. If the sensor has a systematic error, a Kalman filter won't help you.
Basically, the Kalman filter extrapolates an expected value and compares that to the next measurement. The output is a combination of the two. If the measurement jumps left and right, the filter will dampen those jumps. Besides thermal noise, a typical source of such noise is the quantization noise of an analog-digital converter. This kind of noise can be reduced by a Kalman filter.
Other kinds of errors like offset errors or linearization errors cannot be caught by a Kalman filter.

So one single Kalman filter can have many inputs, i.e. one for every sensor? Or does a single kalman filter have to be designed for each sensor?
So it can be used for IRS as well without any problem? (I mostly found it in INS online)

As long as the bias is observable, it is perfectly possible to do bias estimation and compensation in a Kalman filter.

@DeltaLima: As long as the bias is known, you need no fancy Kalman filter to account for it. If it is unknown, the filter won't be of any help.

The Kalman filter can be used to estimate the magnitude of the bias. The bias is often not directly measureable, but is its magnitude is often determinable over time. By including the bias in the state as a state variable the overall accuracy of the state estimation can be improved. If you have for example and one dimensional system where you can measure the position with an unbiased but very imprecise sensor, and the acceleration with a biased but precise sensor, a Kalman filter can be made that will give you a) accurate position, b) accurate acceleration, c) the bias of your accelerometer.

@DeltaLima What you describe is a low pass filter for the accelerometer where the long-term mean is integrated and compared to the position change. Do it several times to account for low position precision and you get the bias.

@PeterKämpf the low pass filtering and integration is happening in the Kalman filter (KF), in this specific case. Yes in this case it can be done without a KF. The example I gave was to illustrate that a KF is generally useful to estimate the state of something that is not directly measurable (i.e. an internal state such as a sensor bias), but can be inferred from the system outputs. The measure of how well this internal state can be inferred is called observability. The concept of observability originates from Rudolf E. Kálmán, the father of the KF.


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Are there any hybrid electric planes?
Are there any hybrid planes (planned), or would this be impossible because we don't have big enough batteries?

You might find this YouTube video by Real Engineering interesting: Are Electric Planes Possible?

the main problem with hybrid/electric aircraft is that the batteries and dual propulsion systems add considerable mass while taking up considerably internal space, leaving an aircraft with very limited carrying capacity, performance, and range for the same cost.

There are experimental electric planes. Some are promising enough that they might end up useful as trainers and private GA flown for the love of flying.
Long-range electric will not work. The electric equivalent of the Breguet equation is R=L/D*E/W*n/g, where E is stored energy and n is propulsive efficiency. For a 100% efficient L/D=20 aircraft that is 100% battery with 250 Wh/kg cycle depth, that's 20*250*3600*1/9.8=1.8*10^6 meters, or 990 nmi. This is the hard limit. With 80% efficient props and real world factors, you can expect 5-8 nmi for each % takeoff weight dedicated to batteries.
Hybrid aircraft are, even on paper, only moderately interesting. Aircraft throttle in cruise at 45-75% for GA, 70-90% for small jets, and 80%-95% for long-haul widebodies. This is due to the engines "self-throttling" in a way - power and fuel consumption reduce due to lower air density as you climb.
So major airliners have nothing to gain from going hybrid, they can only shrink their engines by 5-10% with a hybrid system. This is very different from cars, which run duty cycles as low as 10%.
And there are no start-stops or regenerative braking to recover energy in flight. More precisely, aircraft already use regenerative braking - by pitching up or deploying flaps, speed gets traded for lift. So that braking energy is already being harvested, and stored as altitude (potential energy).
Smaller propeller aircraft could replace up to 30% of their power, so it's less cut and dry. However, when you want full throttle, you often want it for a while, like in climb. The only way for a non-plug-in hybrid to save energy is to use a lighter/smaller engine, and it's difficult to shrink enough to offset the hybrid system's weight.
A plug-in hybrid could benefit from the lower cost of electricity vs avgas, but fuel averages to less than a third of private flying expenses. Pure electrics have a shot at making flying more accessible through simplicity. With no fuel, very simple and reliable engines, it makes sense to relax the rules, like is done for ultralights. Hybrids have all the complexity of a piston-engined plane and then some.
The hybrid route makes sense for cars. The only safety-critical parts of a car are steering and brakes. Engine power is almost arbitrary, most hardware is just nice to have, and there's the universal failsafe of pulling over. In a plane, things need to work. Two systems that both have to work to fly safely is a complication and will likely increase costs.
Alternately, either system needs to supply takeoff thrust on its own. That could work in the 19-seater class, if the authorities accept a hybrid "twin"-engine single prop as sufficient redundancy. But there's a lot of "ifs" in this.
In a zero-weight scenario, some military aircraft (fighters, naval) could benefit from a hybrid system, as they have excess power like cars do. That's where reality hits: for given output, electric motors are lighter than car engines, but much heavier than aircraft jet engines. Since they're not lighter, there's nothing to be gained.

Maybe there would be no advantage for mankind, but for environment by saving CO2

May be worth noting that most hybrid cars recharge their batteries via regenerative braking and that's a big part of their efficiency; I don't know whether a similar method could be applied to planes.

@Squareoot Unless you're making very short flights, a hybrid engine primarily charges its battery from a gasoline engine. So there's little CO2 savings without an increase in efficiency. The answer explains why that's the case for cars, but not for aircraft. A purely electric plane would help, but that's a huge engineering challenge. Or running a plane with a biofuel as the USAF is experimenting with, a rare case where national security and environmentalism coincide. https://www.scientificamerican.com/gallery/military-green-us-air-force-flies-on-biofuel/

I think the only niche where a hybrid would make sense is in analogy to the Chevy Volt:  you size the batteries to do the ~1hr flights typical of a lot of flying, and have gas to fall back on/do long range flights with/fly to where charging isn't practical, but filling up with gas is.

You say that the electric engines of a hybrid only add complexity and thus reduce reliability. But what if they work independently and are able to power the aircraft alone over short distances? Then it would be additional redundancy, which would be especially useful in small, single engine planes.

@Michael As I've mentioned, if either system can do takeoff thrust OEI, it adds redundancy. But engine redundancy is only required with 10+ pax in the US or even more elsewhere. Aircraft engines are reliable enough that engine failure in singles accounts for very few incidents. Small planes can glide to a landing, except in takeoff or over-water failures. Whether a hybrid-twin single-prop will be accepted for 19-pax operation deserves a separate question.

Re, "A plug-in hybrid could benefit from the lower cost of electricity vs avgas." I drive a plug-in hybrid (Cheverolet Volt). The battery weighs about 450 lbs. It can power the car for approximately the same distance as a gallon and a half (12 lbs.) of gasoline.

@Walt Short version is, there is no opportunity for regenerative braking in flight. It is possible to recover energy - that's how the RAT works - but engine thrust is positive in all phases of a normal flight. Even upon landing, the thrust is reversed if possible, which still requires power going into the engine. The few windows for energy recovery amount to <1% of the total, probably under 0.1% even.

@Squareoot - also electricity stills needs to be generated somewhere if no engine is used for charging, such as a power station, which usually have some impacts as renewables are not widely used currently.

There are a number of small (ultralight, Light Sport categories) aircraft that run on pure battery power for anywhere from a few minutes to (as I recall) nearly an hour of powered flight -- a couple of these are essentially motor gliders, so they can extend the total flight time to multiple hours with soaring flight.
Larger hybrid aircraft have been proposed, even in to the regional airliner class -- they'd use small, efficient jets or turboprops, just adequate for cruise, augmented by electric ducted fans or propellers for takeoff thrust, or alternately shaft turbine generators driving pure-electric propulsion fans, augmented with batteries for takeoff power; the result would be, as with a hybrid car, the ability to install a "too small' engine that burns much less fuel, and still get acceptable performance.

Zunum Aero has a great article [here][1] on their entry into the hybrid market for a 12 passenger regional plane.  Goes into pretty good depth on how the plane will work.  [1]:https://spectrum.ieee.org/aerospace/aviation/zunum-aeros-hybrid-electric-airplane-aims-to-rejuvenate-regional-travel

"Smaller engine to burn less fuel" - that's the idea. However, modern jets could lose less than 20% in engine size before they have to cruise lower and face more drag. And such a reduction is not 20% less fuel burn, but just 4-5% less. It's quite questionable if hybrids ever get a niche. Full electrics will.

There is a company call Bye Aerospace here in Colorado that recently celebrated a successful first flight of their "Sun Flyer" prototype, an all-electric 2 seat trainer. I believe they are planning a 4 seat version as well. Check 'em out!

This is interesting, but since it's all-electric it doesn't seem to answer the question about hybrid aircraft.

Actually, NASA just announced a new X-plane program. While they haven't selected a design yet, it looks like a hybrid-electric system is one of the designs they will try to build see here. The point of the hybrid system in this case isn't so much about providing additional thrust from an efficient system, but rather to use electricity to transfer power to where it is needed for drag reduction.

That program does not use a hybrid system as used in cars, it rather uses a hybrid system as used in submarines with a turbofan charging batteries which in turn power an electric engine. I wonder how they think to save fuel that way, all it does it increase the mass of the aircraft significantly

Not sure there are any batteries in there at all. The electric system there acts as more of a means to transfer power across the airframe than to preform any regeneration or the like. Drive shafts would be difficult to use there and electric motors are fairly light. You have to remember that the rear nacelle only houses a low pressure fan, there is no need for complex cooling systems and high pressure containment that happens at the back of a turbine, therefor lightweight materials can do the trick easily. Wouldn’t be surprised to hear that it only takes one person to lift that fan.

Even without batteries, there is the extra mass induced by the additional equipment, the drag induced by the extra external fittings, etc. etc. Nice concept in theory, but the practicality seems dubious.


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What materials are used to make up a combustion chamber?
What type of materials are used to make up the different sections such as the linings of the combustion chambers in a gas turbine engine. Do these type of materials vary for the different types of gas turbine Engines such as the multiple-can type, annular and cannular.

If you are asking about combustor liners specifically (as opposed to the hot section in general), the ones I am familiar with are cobalt-based superalloys.

This is more of an engineering question than an aviation question, but since some aviators may be interested in knowing exactly what is in those turbines I will answer.
There are three main types of refractory alloys commonly used for high-temperature components in turbine engines. They are:
ODS (oxide dispersion strengthened superalloys)
CMC (ceramic matrix composites)
intermetallic post transition alloys
Of the intermetallics that are used, there are two main types commonly used: NiAl (nickel aluminum) and TiAl (titanium aluminum).


text:
Is there a tool or site where I can see wind vectors overlaid on a prognostic chart?
I'm hoping to find a source where I can see wind vectors overlaid on a prognostic chart, to visualize how the wind moves around the pressure systems and fronts.
Curious if anyone knows of illuminating and fun weather data visualizations e.g.
https://earth.nullschool.net

I'm voting to close this question as off-topic because it would probably be better on Earth.SE.

Apart from being probably off-topic, the first part of this message feels like spam to me

@Federico: not spam. Search that like in Google?

@Ron Beyer this IMO would be a very helpful resource for pilots

regarding what Ron Beyer said, we already had this discussion (https://aviation.meta.stackexchange.com/q/3215/1467 ) the outcome was: if the aviation aspect it is not prominent, it is off-topic.

I like www.windy.com

Most pilots here in the states get their weather data from NOAA (The national weather service) you can find all of their charts on their site here.
Localized aviation weather is usually reported out of airports and can be found via their METAR's.
For visualization apps like Foreflight and Garmin Pilot allow certain overlaying of data onto a map (these are however paid services).


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Can an ASEL class-rated private pilot without a T/W endorsement count T/W hours towards FAA flight time requirements?
I am an ASEL rated private pilot without a tailwheel nor a complex aircraft endorsement. I have been flying with an aerobatics pilot in his Pitts and his Bonanza for ~10 hours over the last month.
Although I have not confirmed with him, I suspect (and for the sake of discussion, we can assume) that he is not a current certificated flight instructor (I suspect this because he has never offered to sign my log book nor has he suggested that I log the hours as dual).
My question is twofold:
(Q1) pertaining to the requirements to log PIC time given in 61.51(e) do my hours in the Pitts and/or the Bonanza qualify?

FAR 61.51(e)
(1) A sport, recreational, private, commercial, or airline transport
  pilot may log pilot in command flight time for flights-
(i) When the pilot is the sole manipulator of the controls of an
  aircraft for which the pilot is rated, or has sport pilot privileges
  for that category and class of aircraft, if the aircraft class rating
  is appropriate;
(ii) When the pilot is the sole occupant in the aircraft;
(iii) When the pilot, except for a holder of a sport or recreational
  pilot certificate, acts as pilot in command of an aircraft for which
  more than one pilot is required under the type certification of the
  aircraft or the regulations under which the flight is conducted; or
(iv) When the pilot performs the duties of pilot in command while
  under the supervision of a qualified pilot in command provided -
(A) The pilot performing the duties of pilot in command holds a
  commercial or airline transport pilot certificate and aircraft rating
  that is appropriate to the category and class of aircraft being flown,
  if a class rating is appropriate;
(B) The pilot performing the duties of pilot in command is undergoing
  an approved pilot in command training program that includes ground and
  flight training on the following areas of operation -
(1) Preflight preparation;
(2) Preflight procedures;
(3) Takeoff and departure;
(4) In-flight maneuvers;
(5) Instrument procedures;
(6) Landings and approaches to landings;
(7) Normal and abnormal procedures;
(8) Emergency procedures; and
(9) Postflight procedures;
(C) The supervising pilot in command holds -
(1) A commercial pilot certificate and flight instructor certificate,
  and aircraft rating that is appropriate to the category, class, and
  type of aircraft being flown, if a class or type rating is required;
  or
(2) An airline transport pilot certificate and aircraft rating that is
  appropriate to the category, class, and type of aircraft being flown,
  if a class or type rating is required; and
(D) The supervising pilot in command logs the pilot in command
  training in the pilot's logbook, certifies the pilot in command
  training in the pilot's logbook and attests to that certification with
  his or her signature, and flight instructor certificate number.
(2) If rated to act as pilot in command of the aircraft, an airline
  transport pilot may log all flight time while acting as pilot in
  command of an operation requiring an airline transport pilot
  certificate.
(3) A certificated flight instructor may log pilot in command flight
  time for all flight time while serving as the authorized instructor in
  an operation if the instructor is rated to act as pilot in command of
  that aircraft.
(4) A student pilot may log pilot-in-command time only when the
  student pilot -
(i) Is the sole occupant of the aircraft or is performing the duties
  of pilot of command of an airship requiring more than one pilot flight
  crewmember;
(ii) Has a solo flight endorsement as required under § 61.87 of this
  part; and
(iii) Is undergoing training for a pilot certificate or rating.

My interpretation of 61.51(e) is that because I am not yet allowed to fly either plane solo (i.e. I don't have my endorsement for either) then without a current instructor or ATP certificated pilot, I'm out of luck. Any other perspectives/interpretations? Am I missing something?
(Q2) pertaining to the aeronautical experience requirements for an initial ASEL commercial certificate can these hours be credited towards my required 250 hours given in in FAR 61.129(a)?

FAR 61.129 (a) For an airplane single-engine rating. Except as provided in
  paragraph (i) of this section, a person who applies for a commercial
  pilot certificate with an airplane category and single-engine class
  rating must log at least 250 hours of flight time as a pilot that
  consists of at least...

The language in 61.129(a) seems to indicate that the 250 hours need to qualify as flight time where

FAR 1.1 Flight time means:  (1) Pilot time that commences when an aircraft
  moves under its own power for the purpose of flight and ends when the
  aircraft comes to rest after landing;

and

FAR 61.1 Pilot time means that time in which a person -
(i) Serves as a required pilot flight crewmember;
(ii) Receives training from an authorized instructor in an aircraft,
  flight simulator, or flight training device; or
(iii) Gives training as an authorized instructor in an aircraft,
  flight simulator, or flight training device.

I don't suspect that I am a required pilot flight crewmember; nor is he an authorized instructor (by assumption); so again, am I out of luck?

Downvoted for obscene language.

Upvoted because this is a good question.

@RalphJ -- the language issues are fixed now

It is a good question, however I think that this may be something that your FSDO is going to have to answer. I suspect that the answer is no, because you would not be acting in the PIC role because you are not rated (nor are you a required crew), you are basically a passenger being allowed to manipulate the controls (well under the PIC's rights) who happens to have a PPL.

If you are flying with an ATP pilot, they still cannot endorse your logbook.  They are only an authorized instructor when qualified as such under 121 or 135 and only for their companies training program.

As long as you are the sole manipulator of the controls, I would count that as flight time.  Pilot time is only useful for ATP qualifications (1500 hours of pilot time).  PIlot time is gained when you can log flight time, or receiving training in an flight simulator or fight training device.

First, can you log PIC time in the tailwheel? Yes, you can log PIC tailwheel time but only where you were the sole manipulator of the controls. As discussed in this question, the only requirement is to be "rated" in the aircraft, which is explained in this FAA legal interpretation:

The FAA previously has stated the term "rated" as used in 61.51(e),
  refers to the pilot holding the appropriate aircraft ratings
  (category, class and type, if a type rating is required)

Your Private ASEL qualifies you in category and class and there's no type rating needed for the Bonanza or Pitts. So you can log PIC time under 61.51(e)(1)(i) for the time where you were sole manipulator of the controls. You can't log training (dual) time though, unless the other pilot is a CFI and endorses your logbook.
Second, can you use the time towards a commercial rating? This is an interesting point: the definitions in the regulations imply no, as you said, and I can't find any FAA interpretation on it. However, my personal experience is that DPEs were only interested in the PIC time in my logbook. I've never heard of a DPE or anyone else making a distinction between "PIC time" and "pilot time", and AC 61-65 doesn't seem to have any specific guidance for examiners on it, apart from checking that applicants have the required "flight time".
But a DPE might still ask you about logging PIC time without being qualified to act as PIC; that seems like a reasonable question for an oral test, especially for an instrument or commercial checkride. If he spots tailwheel time in your logbook without a tailwheel endorsement, it would be a great lead-in to the topic.
Maybe someone else will find a definitive answer on the "pilot time" question, but if there's nothing official from the FAA so far then you could request a legal interpretation from the FAA Chief Counsel. However, for the sake of your fellow pilots I strongly suggest that you don't do that. If the FAA comes back with the 'wrong' answer, it could create restrictions that didn't previously exist. The Mangiamele interpretation is notorious in that regard because it stopped private pilots from claiming travel expenses from their employers that were previously allowed, or at least tolerated. You really don't want to be the guy who makes it harder for people to get a commercial certificate.

Thanks for the references; the distinction between being "rated" for the aircraft and being "authorized" to act as PIC is at the heart of my concerns; the instance of the non-instrument rated pilot logging time under IFR was illustrative.

In my limited experience I find that the language used in the FARs is at times ambiguous; perhaps this is due to a naive understanding, perhaps this is somewhat by design, or perhaps both.
Specifically in 61.51 it states that a pilot may log PIC "flight time" when acting as sole manipulator of controls if s/he is properly rated in the aircraft BUT "flight time" is defined as "pilot time" and in the relevant situation(s) explored above its clear that logging PIC hours may not suit the definition of flight time.

Which would lead one to conclude, as you note, a distinction between "pilot time" and "PIC time"; not going to be the one to press the FAA on this because I'd rather log the hours than risk omitting them from my subset of 250. It's not the first time, though, that I've noticed "grey area" seemingly built into the FARs

The link to the "Mangiamele interpretation" above is broken -- here is an updated link

@user2070305 You can actually update the link yourself by editing the original answer.  I've gone ahead and done so for you.


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How can I use a Bluetooth headset in an ATR 72 cockpit?
Is there any device available to connect a pair of Bluetooth earphones to the audio system of an ATR 72 aircraft, to receive and transmit on the radio?
The stock headsets are horrible. I own a David Clarke headset too but the cables are a little annoying. If there's a solution to use a Bluetooth headset with a mike to replace the headset in the aircraft it would be lovely.

Flying Magazine reviewed headsets for pilots back in 2013 and four years ago there were already bluetooth-capable headsets in the market from Bose, David Clark, Sennheiser and Lightspeed. You might want to start there...